The invention relates to improvements in winders for paper making machines and to vibrational dampeners therefor and to improvements in mechanisms for damping the vibrations of various rotating members such as rolls used on a paper making machine.
In a winder for a paper making machine, one type of structures involves a pair of drums on which a paper roll being wound is supported. Above the roll being wound and in engagement with the surface thereof is a rider roll which rests on top of the roll being wound to help control the tension with which the web is wound into the roll and the hardness of the roll. These may be provided for either relieving the weight of the rider roll or for increasing the pressure at which it engages the roll being wound.
During relatively high speed winding operations, the rider roll tends to bounce and vibrate, and this may occur in any type of winding process, such as for paper, plastic, cloth or any continuous web of material. The bouncing and vibration has disturbing effects on the roll being wound in that it causes bumps and ripples and uneven winding and must be eliminated, particularly because its effect is accelerated with increase in winding speeds.
This type of rider roll, and other rolls in the paper making operation, can vibrate at a natural frequency coincident with the degree of freedom represented by the mass-elastic system through a process of self-excitation. Also, its mass-elastic system can have several degrees of freedom, dependent upon the structure thereof, and thus several natural frequencies. The natural frequency of each degree of freedom is also a function of the mass of the winding roll, and in the case of a winder, at a given instant of time during the winding process, and the paper elasticity or spring formed through contact with the rotating roll. It has also been recognized that the rider roll assembly responds to the vibration of the winding itself much like a follower. In order for the assembly to resist the winding roll vibration, it must either be sufficiently stiff, which is impractical in many designs, or it must have its vibrations damped. It is accordingly an object of the present invention to provide a mechanism which is capable of dampening the vibrations in a rider roll and eliminating the defects in the wound roll due to such vibrations.
In accordance with the principles of the present invention, a dampening device is applied to the rider roll wherein the device has an elongate hollow tube which fits into or is attached at one side of a beam which is coextensive with the rider roll. The rider roll is mounted at its ends and bearings on the beam. Within the outer stationary hollow tube or cylinder is an inner beam preferably of circular cross-section and a continuous elastic tubing is annularly or spirally wound around the inner beam. Between the outside of the tubing and and the inner surface of the tubular member is a layer of steel slats which extend parallel to the axis of the beam. To the outer surface of these slats is laminated a sheet of fibrous material. The inflatable tubing is sealed at one end and inflated with a desired air pressure from the opposite end to force the slats outwardly against the inner surface of the cylindrical tube.
This arrangement provides for energy absorption transferred from the beam to the cylinder by the shearing action resulting from the differential strain between the fibrous material and the cylindrical housing when flexural motion occurs, and also from the deformation of the viscoelastic tubing resulting from the inner beam and cylindrical housing having different mode shapes.
The first means of energy absorption referred to above is unique in that it provides the conditions of optimum pressure on the fibrous material, uniform pressure on the fibrous material and no effect of relaxation of the fibrous material.
The second means of energy absorption referred to above is the application by unique means of the classical auxiliary mass damper theory. This requires that the first natural frequency of the inner beam must be between 80% and 125% of the responding frequency of the rider roll beam. Since the responding frequency of the rider roll beam is the function of the mass-elastic system degrees of freedom, thus a function of the winding roll in contact with the winder drums and rider roll, the natural frequency of the inner beam must be designed to encompass a specific frequency range which, in turn, is a function of the mass ratio between the inner beam and rider roll assembly. The mass of the inner being from 2.5% to 12.5% of the mass of the rider roll assembly. The combined assembly of the vibration dampener, which includes the inner beam, wound tubing and slats, is that it provides adequate dampening over a wide frequency range. This damping means may be adjusted to optimum damping conditions by changing air pressure in the tubing. The vibration damper is proportioned along the length of the rider roll assembly in manner such that increments of length subjected to the largest amplitudes of vibration will be subjected to the largest damping forces, creating a damping means quite frictional in nature. Thus, this damping means is expected to be responsive mainly to vibration amplitude and, therefore, somewhat frequency independent.
It is, therefore, a further object of the present invention to provide an improved roll assembly and frequency dampener in a combination which is not complicated in structure and which is capable of operation over a wide range of speeds and can be utilized in a variety of locations in a paper making machine or other machinery having vibration creating rolls.